Processes for converting olefins to aldehydes and/or alcohols by the reaction of an olefin with carbon monoxide and hydrogen in the presence of a suitable catalytic complex in either batch or continuous processes are well known in the prior art, and are commonly referred to as oxo or hydroformylation processes.
Catalytic complexes commonly employed in the above processes are ex situ or in situ formed complexes of a transition metal, carbon monoxide, hydrogen and a suitable ligand, with excess ligand preferably being employed in the subsequent hydroformylation reaction. The metal employed is preferably a Group VIII metal, and even more preferably, is selected from rhodium, cobalt and iron. Rhodium is especially preferred since catalysts prepared therefrom permit the employment of commercially more desirable operating conditions. Suitable ligands will be described in greater detail hereinafter.
In the operation of the aforesaid process, it has been noted that the catalyst tends to exhibit relatively different initial activities and to undergo deactivation at relatively different rates depending upon the source of the ligands. These differences are believed to be attributable to impurities present in the ligand employed. More specifically, an impurity can bind directly with the Group VIII metal, e.g., rhodium, resulting in a reduced initial activity. Moreover, impurities can also catalyze aldehyde heavy end formation, resulting in the slow steady deactivation of the catalyst.
Since the catalyst life has a significant effect upon the commercial economics of the hydroformylation process due to the high catalyst cost and the necessity of purging the system to replace the catalyst, it is important to select the ligand permitting the formation of a catalyst which will be operable for the longest time period, i.e., the ligand having the greatest purity.
Prior to the present invention, no suitable method has been available for determining the relative purity of ligands of the same chemical structure obtained from different sources, thus providing a means whereby one might select an appropriate ligand for use in the formation of hydroformylation catalysts, or for other purposes.